The present invention relates to improvements in the art of producing melt-blown microfibers of plastic wherein a plurality of laterally spaced aligned hot melt strands of polymeric material or the like are extruded downwardly and immediately engaged by a pair of heated pressurized angularly colliding heated gas streams.
In typical arrangements heretofore used, the gas streams each were in a flat sheet-like configuration and on opposed sides of each of the strands. The streams functioned to break up the strands into fine filamentous structures attenuating the strands for strength. Examples of constructions of this type are shown in copending applications of Langdon, Ser. No. 463,460 and Daane, Ser. No. 463,459.
In structures such as those shown and disclosed in the above applications, and also in other contemporary developments, two flattened gas streams were employed to laterally engage the fine streams of plastic as they were extruded from the small die openings. Gas temperature, pressure, volume are controlled and maintained uniform for obtaining the optimum effect on the plastic strands. However, difficulties in production caused by nonuniform temperature gradients and problems in elongation occured in certain circumstances and various efforts have been made to correct these difficulties and to improve the quality of the strands formed and the speed of production of the mechanisms and certain improvements are disclosed in the above referred to copending patent applications.
One way of improving the quality of the product produced is to produce a better velocity component of the flow of gas in the direction of the extruded fibers produced by the die. For various reasons, physical limitations are encountered in the relative velocity of the flow of gas. It has been discovered that high velocities approaching or exceeding sonic velocities are desirable. It has also been felt that it is essential to improved product quality and speed of production to obtain a relationship between the gas and plastic flow that obtains optimum contact, both for the attenuation effect of the gas on the plastic and the heat transfer relationship therebetween.
It is accordingly an object of the present invention to provide an improved mechanism and method for producing plastic microfibers which are extruded and engaged with a high velocity flow of gas wherein the gas flow path is controlled relative to the plastic flow to obtain improved product and improved production speed.
More particularly, an object of the invention is to provide a mechanism and method for an improved attenuation effect and improved contact between the flow of gas and flow of plastic in a process embodying blown microfiber production.
A further object of the invention is to provide an improved die head construction incorporating the flow of gas for the production of blown microfibers wherein increased gas velocities can be employed.
A still further object of the invention is to provide an improved extrusion head structure for producing melt-blown microfibers wherein the heat transfer relationship and attenuation relationship between the gas and fibers is improved and wherein the flows are parallel to each other at the point in time of contact therebetween and for the duration of contact.
Other objects, advantages and features, as well as equivalent structures and methods which are intended to be covered herein, will become more apparent with the disclosure of the preferred embodiments in connection with the teachings of the principles of the invention in the specification, claims and drawings, in which: